Switchable support element

ABSTRACT

A support element (1) is designed to be disconnected by a lift movement of a control cam, and includes radially movable coupling elements (12). To disconnect the support element (1), the coupling elements (12) are moved inwards by hydraulic medium, while at the same time a piston (4) communicating with the finger lever is held in cam-distant position by the hydraulic medium.

BACKGROUND OF THE INVENTION

The invention relates to a switchable support element for a cam-actuatedfinger lever of a valve drive for an internal combustion engine, havinga hollow cylindrical housing disposed with its outer jacket in areceiving bore of a cylinder head, with a piston disposed therein whichis axially movable at least relative to the housing and supported by acompression spring.

Such a device is known from DE-A 40 00 531, and includes also a hollowcylindrical housing connected together with a hollow cylindrical innerelement and disposed inside a cylinder head of an internal combustionengine. Both elements are biased by a compression spring in direction ofdischarge. The housing is provided with an oil supply line for enablingin conjunction with a control edge of the inner element and independence on an oil charge in the inner space enclosed by the twoelements a lifting/lowering of the inner element relative to the housingand to thereby shut down or vary the stroke of the gas exchange valvewhich communicates with the support element via the finger lever. Thedifferent oil charge is effected by turning the housing relative to theinner element, since thereby different inlet flow cross sections areprovided via the control edge.

The valve drive tappet known from above-stated DE-A 40 00 531 has thedrawback that the oil cushion does not allow a formfitting, i.e. adefined cutoff/decrease of the valve lift. This oil cushion exhibits, onthe one hand, a certain minimum compressibility, and on the other hand,oil losses can be expected across the sliding surface of both elements.Furthermore, it is anyhow difficult to achieve a precise strokeadjustment and fixation in this position by means of oil pressure, sincethe adjusted height is maintained directly through the oil pressure, andtoo many additional parameters which are hard to manage have an impact.In addition, the housing must be acted upon by mechanical forces toeffect a rotation so that again a drive is needed. Other operationalcondition may also be conceivable, by which the gas exchange valve canbe activated when the internal combustion engine is shutdown, i.e. thevalve should not be turned off. The above solution makes no provisionstherefor, since the aforementioned adjustment device collapses when theinternal combustion engine is shutdown, thereby deactivating therespective gas exchange valve.

There are other switchable support elements known in the art (DE-GM 9319 435.8), which effect a locking of the components for coupling thesupport element to the stroke motion of the control cam via radiallydisplaceable pistons. In the decoupled state, a respective housing partexecutes an idle stroke during lifting of the control cam.

SUMMARY OF THE INVENTION

It is the object of the invention to improve a switchable supportelement in such a way that it exhibits a high stiffness when itscomponents are locked, while in the disengaged state previouslyencountered friction losses are minimized and, at the same time, thesupport element can be disengaged at high rotational speeds.

This object is attained according to the invention by disposing in thepiston at least one bore extending radially or as a secant and alignedwith a respective other bore during the base circle portion of the cams,with at least one coupling element being arranged in one of the boresand moveable in the direction of the respective other bore forselectively coupling/decoupling of the support element with the fingerlever secured thereto from a stroke motion of the control cam; byproviding in a cam-distal bore of the piston an inner element which isaxially moveable with respect to the other bore, wherein a cam-proximalend face of the inner element is spaced at a distance during the basecircle portion of the control cam and in coupled state of the supportelement relative to a base of the bore, at formation of a piston space,which distance corresponds to the desired cutoff stroke of the fingerlever; by positioning the piston to rest with its base in the decoupledstate of the support element against the end face of the inner element,with the coupling element being completely displaced in one of thebores; and by arranging between a cam-proximate end face of the pistonand a corresponding end face of the housing an upper annular space whichcan be filled with hydraulic medium for effecting a decoupling inopposition to the force of the compression spring, with the annularspace having a height which at least corresponds to the desired cutoffstroke of the finger lever. It is not necessarily required, butdesirable, that in a decoupled state, the base of the piston rests uponthe end face of the inner element; it is, however, of importance toeffect a complete disengagement of the inner element from the camregion.

The afore-stated measures effect, on the one hand, a locking throughformfitting engagement, with the entire support element exhibiting ahigh stiffness. This high stiffness is particularly advantageous for theentire valve drive dynamics at high rotational speeds. At the same time,it is possible by using simple means, eliminating additional radiallydisplaceable coupling elements, to completely disengage the supportelement with the finger lever secured thereto from the lifting motion ofthe control cam. The complete decoupling effects a decrease of thefriction losses encountered in conventional devices as a result ofcontinuous contact between the finger lever and the cam. At the sametime, the force provided by a compression spring disposed in the supportelement and acting upon the finger lever in the event of feedback viathe support element, can be reduced significantly. This decrease of thespring force effects a cutoff of the respective gas exchange valves evenat the highest rotational speeds, since otherwise the aforementionedcompression spring would have to be sized to be very strong for theserotational speeds. It is provided that the support element is in itscoupled state when the hydraulic medium is not active, therebyguaranteeing operability under emergency conditions. While it ispossible and also provided to couple via hydraulic medium and todecouple via the force of corresponding springs, the force of thecompression spring may equally be replaced entirely by hydraulic medium.Instead of employing the compression spring and the hydraulic medium,respectively, the components may also be locked by magnetic,electromagnetic or other mechanical means which are not described inmore detail.

Preferably, two diametrically opposed hydraulic pistons are employedwhich are acted upon by hydraulic medium radially from the outsidethrough corresponding supply bores. This configuration according to theinvention guarantees that no additional or only a minimum of additionalinstallation space has to be provided for the support elements.

Movement of the hydraulic piston in a radially inward direction islimited by a stop element located in the center of the bore.

The air mass enclosed in the piston space in cooperation with thechannel extending into the lower annular space provides a "soft" impactfor the base of the extension upon the end face of the inner element,since the channel is so dimensioned that the air mass entrapped in thepiston space acts as an air cushion. However, several such channelsdistributed around the circumference may also be envisioned. Instead ofthe channel on the end face and the bottom, respectively, correspondingdamping elements, for example elements made of plastic material, mayalso be employed.

In accordance with the invention, the provided "hydraulic" retention ofthe piston of the support element in the decoupled position makesadditional mechanical coupling elements unnecessary. The implementationof the invention is not adversely affected by the possibility of the oilmass flowing into the upper annular space and possibly mixing with theair mass contained therein.

It is especially advantageous to provide the support element accordingto the invention simultaneously with a conventional hydraulic clearancecompensation element. It is, however, also possible to omit thehydraulic clearance compensation element and to resort to other knownmechanical clearance compensation elements.

According to another feature of the present invention, a needle is soreceived in a radial recess of the main piston as to project beyond therecess on both sides for cooperation with corresponding longitudinalgrooves formed outside on the inner element and the housing. The needleis mainly intended to ensure that the piston, the housing and the innerelement do not rotate with respect to each other. The outer jacket ofthe housing is typically fixedly installed in the receiving bore. Anupper end face of the longitudinal groove in the inner element, inconjunction with the needle, forms an additional stop/transport safetymechanism for the inner element.

A simple seal of the upper annular space is effected via an axial flangeof the housing at the cam end, with the piston being formed with ahollow cylindrical extension axially projecting beyond the flange.Advantageously, at least the housing is made of thin sheet steel ofdeep-drawing quality; however, at least one of the components of thesupport element may also be made from plastic material or lightweightmaterial.

The support element or its piston is preferably connected to the fingerlever through a clamp connection; however, other connection means, suchas screws or the like, may also be used.

In accordance with the invention, the distance between the cam-proximalend face of the inner element and the base of the bore is so selected asto effect a complete shutdown of the finger lever via the supportelement. If partial lifts are desired, the respective distance mayconceivably be minimized. It may however also be possible to realizestepped lifts, effecting for example a rotation of the inner elementwith respect to the piston, and creating respective stops for the strokevia the needle of the piston.

The invention is not limited to the features set forth in the claims.Contemplated and provided are also combinations of individual claimfeatures and combinations of individual claim features with the listedadvantages and the features of the embodiment.

BRIEF DESCRIPTION OF THE DRAWING

The invention is now described with reference to the drawing, in whichFIGS. 1 to 3 illustrate the various decoupling stages in two rotatedviews a and b of the support element according to the invention and FIG.4 shows a general sectional overview of a cylinder head construction,incorporating a support element according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, the basic features of the switchable support elementwill be described with reference to FIGS. 1a and b, with a descriptionof the FIGS. 2a, b and 3a, b restricted to explaining the differentcoupling states.

FIG. 1a shows a switchable support element 1 which includes a hollowcylindrical housing 2 disposed with its outside jacket 3 in a receivingbore of a stationary cylinder head generally denoted by referencenumeral 50, as shown in FIG. 4. The support element 1 supports one endof a finger lever, generally denoted by reference numeral 51 which is indriving relationship between a control cam 52 and a gas exchange valve53. Interaction between the cam 52, finger lever 51, and valve 53 isgenerally known so that a detailed description thereof is omitted forthe sake of simplicity. Disposed inside the support element 1 is apiston 4 adapted for axial movement with respect to the housing 2. Thepiston 4 is biased by a compression spring 5 in cam direction. Thecompression spring 5 thus acts, on the one hand, upon a cam-distal endface 6 of the piston 4 and, on the other hand, upon a ring element 7.The ring element 7 is in turn connected to one end 8 of an inner element9. The inner element 9 extends in a cam-distal bore 10 of piston 4 andadapted for axial movement therewith.

The inner element 9 includes a bore 11 extending radially. Positioned inthe bore 11 on both ends are coupling elements 12 formed as hydraulicpistons. When the support element 1 is coupled, the coupling elements 12extend simultaneously radially outwards into correspondingly alignedbores 13 of the piston 4. At the same time, the coupling elements 12 areeach spring-biased radially outwards by the force of a respectivecompression spring 14. Radially inward travel of the coupling elements12 is limited by a stop element 15 near the center of the bore 11 ofinner element 9.

A base 16 of the bore 10 of the piston 4 is separated from an end face17 of the inner element 9 by a distance corresponding to the desiredcutoff stroke of the support element 1. Formed between the two faces 16,17 is a piston space 18. The piston space 18 is provided with radialbores 19 arranged around its circumference near the base 16 for allowingair residing in the piston is space 18 to flow into an upper annularspace 20, with the annular space 20 extending between a cam-proximal endface 21 of the piston 4 and a corresponding end face 22 of the housing2. At the same time, the housing 2 is provided with bores 23 inalignment with the bores 19. These bores 23 allow a conduction of afirst partial amount of air from the piston space 18 into the annularspace 20 in a manner to be described later. A ground undercut 24disposed in the region of the annular space 20 may simultaneously beused to conduct air from the piston space 18 into the annular space 20.

The end face 22 of the housing 2 terminates radially inwardly in camdirection in an axial flange 25. At the same time, the piston 4 isguided with a hollow cylindrical extension 26 in the axial flange 25 andjuts outwardly in axial direction beyond the axial flange 25. In thisembodiment, a cam-proximal end face 27 of the extension 26 is providedwith a bore 28 by which a calotte of a finger lever 51 supported by thesupport element 1 can be lubricated.

As illustrated in FIG. 1b, the housing 2 includes an elongated recess29. This recess 29 communicates in the coupling position depicted herewith a ring groove 30 in the outer jacket 31 of the piston 4. The ringgroove 30 simultaneously communicates with a passageway 32, 33 throughthe piston 4 and the inner element 9 for supplying hydraulic medium to ahydraulic clearance compensation element 35 disposed in a bore 34 of theinner element 9. The end 36 of the clearance compensation element 35faces directly a base of the receiving bore of the cylinder head 50.

At the same time, a needle 38 is disposed in a recess 37 of the piston 4and projects outwardly past the piston surface on both sides forpreventing a rotation of the components 2, 4, 9 with respect to eachother. The needle 38 cooperates, on the one hand, with a longitudinalgroove 39 at the outer jacket 40 of the inner element 9 and engages, onthe other hand, in a further longitudinal groove 41 of the housing 2.

After having described the structure of the support element 1 accordingto the invention, the mode of operation will now be discussed in moredetail.

In the FIGS. 1a, b, the support element 1 is depicted in its couplingposition. In this state, there is only applied low pressure to thehydraulic medium at recess 29 for supply of the clearance compensationelement 35. This hydraulic pressure is not sufficient to displace thecoupling elements 12, which are acted upon their outer end face 42 byhydraulic medium via the ring groove 30, radially inwardly into the bore11 against the spring force of compression springs 14 to such an extentthat they completely remain inside the bore 11 and do not project withtheir end face 42 beyond the outer jacket 40 of the inner element 9.

When the pressure of the hydraulic medium to the ring groove 30 isincreased at the recess 29, then the coupling elements 12 shift duringin the base circle portion of the control cam 52 completely into theirbore 11 against the spring force of their respective compression springs14. The piston 4 is moved away from the cam at commencement of the camlift, with air residing in the piston space 18 being conducted into theupper annular space 20 via bores 19, 23. The bore 23 in the housing 2aiding the overflow forms a control edge 43 in the area most distantfrom the cam 52 (see FIG. 2). The bore 23 with its control edge 43 arethereby positioned in such a way that the piston 4 entraps a residualamount of air in the piston space 18 extending to the base 16 when itpasses the control edge 43 on its axially downward motion. Since at thispoint air can no longer flow from space 18 into space 20, a furtherescape of the residual amount of air in the piston space 18 is effectedthrough a channel 44 extending in the bore 10 of the piston 4 axiallyaway from the cam 52. The channel 44 terminates with its cam-distal endin a lower annular space 45 between the inner element 9 and the housing2 for receiving the compression spring 5. The air pushed out of thepiston space 18 can escape therefrom through discharge openings 46distributed around the circumference of the housing 2 into not shownexhaust lines of the cylinder head 50. The cross section of channel 44,including the possibility of having several channels per support element1, is so dimensioned that air can only escape from the space 18 whileperforming compressive work. This provides for a "soft" seating of thepiston 4 (see FIGS. 3a and b) with the base 16 of its bore 10 on thecam-proximal end face 17 of the inner element 9. As can be seen fromFIGS. 2 and 3, the piston 4 releases during its continuing axialdownward motion a partial cross section of the recess 29 which issubject to hydraulic pressure. The hydraulic medium flowing into theannular space 20 through the recess 29 retains the piston 4 in the finalposition shown in the FIGS. 3a, b as a result of the pressure exerted onthe cam-proximal end face 21 of the piston 4.

Should a feedback from the respective support element 1, including thefinger lever 51, to the stroke motion of the respective gas exchangevalve be desired, then the pressure of hydraulic medium at the recess 29is reduced. As a result, the piston 4 can now be moved by the springforce of the compression spring 5 in cam direction. When the upper finalposition depicted in the FIGS. 1a, b is reached (base circle portion ofthe control cam 52), the coupling elements 12 are partially displacedradially outwardly into the bore 13 of the piston 4 by the spring forceof their compression spring 14. Air or air-oil mixture remaining in theannular space 20 can reach the piston space 18 through the bores 23, 19or can escape through the channel 44.

As a result of the support of the compression spring 5 on the innerelement 9 and the piston 4, there is provided a inner closed force fluxof the compression spring 5 in the locked state. Consequently, apossible influence of the compression spring 5 on the operation of theclearance compensation element is eliminated.

The shown disengagement of a gas exchange valve by way of a switchablesupport element 1 is suitable for selective cutoff of individual gasexchange valves in multi-valve technology, in an entire cylindershutdown or even in a shutdown of entire cylinder banks, for example forV-engines.

What is claimed is:
 1. A switchable support element for a cam-actuatedfinger lever of a valve drive for an internal combustion engine,comprising:a hollow cylindrical housing disposed in a receiving bore ofa cylinder head; a spring-biased main piston disposed in the housing andaxially movable relative to the housing, said main piston defining anaxial first bore and being formed with at least a second bore; an innerelement so received in the axial bore of the main piston as to allow arelative displacement between the main piston and the inner element inresponse to an operation of a control cam, said inner element beingformed with a bore which is in alignment with the second bore of themain piston during a base circle portion of the control cam; and acoupling element so positioned in at least one of the second bore of themain piston and the bore of the inner element as to be displaceable in adirection toward the other one of these bores for movement between acoupled state in which the coupling element couples the main piston andthe inner element and a decoupled state in which the coupling element isreceived in only one of these bores and the main piston is disengagedfrom the inner element; said inner element having a cam-proximal endface which is spaced from an opposing end face of the main piston duringthe base circle portion of the control cam and in the coupled state todefine a piston space having a vertical extension corresponding to thedesired cutoff stroke of the finger lever, and with an annular upperspace being formed between a cam-proximate end face of the main pistonand an opposite end face of the housing and so connected as to be permitentry of hydraulic medium to act upon the main piston in the decoupledstate, with the upper annular being defined by a minimum verticalextension which at least corresponds to the extent of a desired cutoffstroke of the finger lever.
 2. The support element of claim 1 whereinthe second bore of the main piston extends in a radial direction.
 3. Thesupport element of claim 2 wherein the second bore of the main pistonextends along a secant.
 4. The support element of claim 2 wherein thepiston space is in fluid communication with the upper annular space. 5.The support element of claim 1 wherein the end face of the main pistonrests in the decoupled state against the cam-proximal end face of theinner element.
 6. The support element of claim 5 wherein the couplingelement includes a hydraulic piston extending in the bore of the innerelement, and at least one compression spring loading the hydraulicpiston in radially outward direction, with the hydraulic piston bridgingin the coupled state an annular interface between the main piston andthe inner element and thereby partially extending in the second bore ofthe main piston, and in decoupled state being so acted upon at itsradially outer end face by hydraulic medium as to shift completely intothe bore of the inner element.
 7. The support element of claim 5 whereinthe main piston is formed with a ring groove in immediate proximity ofthe end face of the hydraulic piston and in communication with acomplementary recess in the housing for supply of hydraulic medium. 8.The support element of claim 1 wherein the coupling element includes acentral stop member secured in the bore of the inner element forlimiting a displacement of the hydraulic piston.
 9. The support elementof claim 3 wherein the main piston is provided in the area of the pistonspace with at least one other bore for permitting a first partial volumeof air to escape from the piston space into the upper annular space whenthe main piston is moved axially downwards, said housing being formedwith a bore in communication with the other bore of the main pistonduring a first stroke phase thereof, wherein the piston space isconnected to a lower annular space radially disposed between the housingand the inner element underneath the piston space by an axiallyextending channel for discharging in a second stroke phase of the mainpiston a remaining volume of air from the piston space into the lowerannular space while performing compressive work, with at least onedischarge opening being provided in a cam-distant section of the housingfor exit of air from the lower annular space.
 10. The support element ofclaim 1 wherein the main piston is biased by a compression springreceived in the lower annular space and extending between a cam-distalend face of the main piston and a ring element secured to one axial endof the inner element.
 11. The support element of claim 1 wherein thehousing is formed with an outer recess in communication with the upperannular space for passage of hydraulic medium at least during the secondstroke phase.
 12. The support element of claim 11, and furthercomprising a hydraulic clearance compensation element received in acam-distal bore of the inner element and having an axial end directlyfacing a base of the receiving bore of the cylinder head.
 13. (New) Thesupport element of claim 7, and further comprising a hydraulic clearancecompensation element received in a cam-distal bore of the inner elementand having an axial end directly facing a base of the receiving bore ofthe cylinder head, said clearance compensation element being suppliedwith hydraulic medium via a passageway defined by the recess in thehousing, the ring groove in the piston and a passage formed in the mainpiston and the inner element and communicating with the ring groove. 14.The support element of claim 1, and further comprising a needle soreceived in a radial recess of the main piston as to project beyond therecess on both sides for cooperation with corresponding longitudinalgrooves formed outside on the inner element and the housing.
 15. Thesupport element of claim 1 wherein the end face of the housingterminates in a cam direction radially inwardly in an axial flange, saidmain piston being formed with a hollow cylindrical extension soprotruding axially beyond the axial flange as to have sections encircledby the axial flange.
 16. The support element of claim 15 wherein thecylindrical extension has a cam-proximate end face provided with a bore.17. The support element of claim 1 wherein at least the housing is madeof thin sheet steel.
 18. The support element of claim 1 wherein at leastthe housing is made by a deep-drawing process.
 19. The support elementof claim 1 wherein the cam-proximate end face of the inner element is sospaced from the opposite end face of the main piston as to realize acomplete cutoff of the finger lever via the support element.